1. Field of the Invention
The present invention relates to a ceramic laminate material or compositional graded ceramic for use in the production of ion and/or electron conducting ceramic products.
2. Description of the Related Art
Perovskite ceramic material in oxygen separation membranes, have the general formula: EQU A.sub.x A'.sub.x' A".sub.x" ByB'.sub.y' B".sub.y" O.sub.3-.delta.'
wherein
x+x'+x"=1, and PA1 y+y'+y"=1, and PA1 .delta. is a number, which renders the composition charge neutral.
Those materials are known from U.S. Pat. No. 5,240,473.
Dense ceramic membranes comprising a non-perovskite material represented by the formula: EQU (Sr.sub.1-y M.sub.y).sub..alpha. (Fe.sub.1-x Co.sub.x).sub..alpha.+.beta. O.sub..delta.
having electron conductivity and oxygen ion conductivity are known from U.S. Pat. No. 5,580,497.
High oxygen ion conductivity of ceramic materials comprising a superstructural form of the cubic perovskite structure, with the general chemical formula: EQU A.sub.x A'.sub.x' B.sub.y B'.sub.y' O.sub.2.5
has been reported in the scientific literature.
It has been observed that perovskite materials with high oxygen conductivity exhibit poor structural stability and high thermal expansion at low oxygen partial pressures leading to limitations when these materials are used in separation of oxygen. In practice a compromise between high oxygen conductivity or high stability must be accepted (cf. "Dimensional Instability of Doped Lanthanum Chromites in an Oxygen Pressure Gradient", P. V. Hendriksen, J. D. Carter and M. Mogensen, in Proceedings of the fourth international Symposium on Solid Oxide Fuel Cells, Ed. by M. Dokiya, O. Yamamoto, H. Tagawa and S. C. Singhal, The Electrochemical Society Proc. Vol. 95-1, (1995)934; "Dimensional Instability and effect chemistry of doped lanthanum chromites", P. H. Larsen, P. V. Hendriksen and M. Mogensen, Journal of Thermal Analysis, Vol. 49, (1997), 1263; and "Lattice Expansion induced strains in solid oxide fuel cell stacks and their significance for stack integrity", P. V. Hendriksen and O. Joergensen, in "High Temperature Electrochemistry: Ceramics and Metals". Proceedings of the 17th Risoe International Symposium on Materials Science (1996), 263).